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P1491

EGR Valve Lift Insufficient Detected.

  • Infiniti
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
4
AreaAuxiliary emission controls
91
FaultThe specific fault in that area

What it means

P1491 on an Infiniti means the engine control unit has detected insufficient EGR valve lift. The commanded opening of the exhaust gas recirculation valve was not matched by the lift or position feedback, or by the expected change in engine conditions. The valve may be sticking, blocked with carbon, or not being driven properly, or its feedback circuit may be faulty. The exact EGR hardware and test method depend on the model and engine.

Symptoms

  • Malfunction indicator lamp on
  • Pinging or knocking under light load or acceleration
  • Rough idle or occasional stalling
  • Hesitation or poor drivability at part throttle
  • Failed emissions test with high NOx
  • Slightly reduced fuel economy

Possible causes

  • EGR valve or EGR passages clogged with carbon, so the valve sticks or cannot lift fullylikely
  • Faulty EGR valve actuator (solenoid or motor) or internal lift/position sensorlikely
  • Wiring or connector fault in the EGR valve, lift sensor or control circuit (open circuit, high resistance, short, corrosion)possible
  • Vacuum leak, split hose or faulty vacuum control component on models with a vacuum-operated EGR systempossible
  • Restricted or blocked EGR feed pipe or exhaust-side passagepossible
  • Fault in the engine control unit driver or an outdated calibration, where the manufacturer lists it as a known cause for the modelrare

How to diagnose

  1. Read all stored and pending codes and the freeze frame data, noting engine temperature, load and speed when P1491 set. Check for other codes that could point to a shared cause.
  2. Check for technical service bulletins or software updates for the specific model and engine.
  3. Inspect the EGR valve wiring, connector and any vacuum hoses for damage, heat damage, corrosion, loose fit or splits.
  4. Using live data, command the EGR valve open and closed if the scan tool allows. Compare the commanded and actual lift or position values, and see whether engine idle changes.
  5. On vacuum-operated systems, check vacuum supply, hose routing and the control solenoid or valve against the workshop manual.
  6. Check the EGR valve's supply, earth and signal circuits and the sensor and actuator resistance against the specification for the model.
  7. Remove the EGR valve and inspect it and the passages for carbon build-up, a sticking pintle or blockage.
  8. After the repair, clear the code and road test, then confirm the lift reading follows the command and the code does not return.

How to fix

  • Clean carbon from the EGR valve and passages if they are serviceable, or replace the valve if it sticks or is worn.
  • Replace the EGR valve, actuator or lift sensor if it fails electrical or functional tests.
  • Repair or replace damaged wiring and connectors, and clean any corroded terminals.
  • Replace split or perished vacuum hoses and any faulty vacuum control component.
  • Clear any restricted EGR pipe or passage, replacing the pipe if it cannot be cleared.
  • Apply a manufacturer calibration update only if a bulletin confirms it for this fault.

Can I keep driving?

Medium severity

The car can usually be driven for a short time, but get it fixed soon. Continued driving can cause pinging under load, poor drivability and higher emissions, and carbon deposits may get worse.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.

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